1. Field of the Invention
The present invention relates to a technical field for detecting a vibration period by using a quartz-crystal resonator.
2. Description of the Related Art
There sometimes arises a need for detecting a period (frequency) of vibration applied to an object. For example, quick warning is necessary, for example, when an earthquake occurs. When the scale of the earthquake is large, its vibration frequency is about 0.01 Hz to about 30 Hz and is lower than vibration caused by daily life vibration, and therefore, if its vibration frequency can be detected, it is possible to discriminate the earthquake from the daily life vibration. However, detecting such a low frequency is difficult.
An object of the formation of capacitance in Patent Document 1 is to stabilize an oscillation frequency of a quartz-crystal resonator and is different from an object of the present invention.    Patent Document 1: Japanese Patent Application Laid-open No. Hei 07-131279